Study says droughts in the Southwest could become more frequent

The researchers used more generalized storm patterns than daily rainfall statistics, and determined that in the years 1979 to 2014, wintertime snow from low-pressure storms in the Pacific Northwest has become less and less common in the Southwest.

Professor Scott Stine of California State University, East Bay, who has conducted some tree studies himself, says it was easy to forget we consider the last 150 years to be normal, but past history shows many periods of drier decades and much drier centuries.

“The weather types that are becoming more rare are the ones that bring a lot of rain to the southwestern United States”, Prein said.

And because only a few weather patterns bring precipitation to the said region, these changes “have dramatic impact”, Dr Prein warned. The research team hasn’t evaluated the link between drought and climate change in the current study but that is the next step for his team, Prein added.

The Southwest is especially vulnerable to any additional drying. Even so, without a steady source of water, even the bigger, stronger storms may still not be enough to provide the necessary water to western regions.

Meanwhile, NCAR researchers calculate an opposite, albeit smaller, effect in northeastern United States, where levels of precipitation appear to be increasing.

Previous studies of tree ring data suggest that there have been a number of “megadroughts” in the region, some lasting for 20 years or more, but the model for life in California now is based on many years of unusually high amounts of rainfall in the area. Only three of these patterns are favorable for rain in the U.S. Southwest, they said.

This shift toward higher pressure in the North Pacific is consistent with climate model runs, which predict that a belt of higher average pressure that now sits closer to the equator will move north.

The sinking air causes the drier conditions over the region and this prevents the development of the moisture-producing systems.

Climate models generally agree that human-caused climate change will push the southwestern United States to become drier. Co-author Greg Holland explained that because of a decrease in the frequency of rainfalls in the Southeast, droughts are being more intense.

To examine this potential connection further, they are studying climate model data for evidence of similar changes in future weather pattern frequencies.